[rtl/otp_ctrl] Small fix on unlock token encode

This PR fix a small issue reported in #4586.

Signed-off-by: Cindy Chen <chencindy@google.com>

hw/ip/otp_ctrl/rtl/otp_ctrl_scrmbl.sv

diff --git a/hw/ip/otp_ctrl/rtl/otp_ctrl_scrmbl.sv b/hw/ip/otp_ctrl/rtl/otp_ctrl_scrmbl.sv
index 06f616d..2f3e2cb 100644
--- a/hw/ip/otp_ctrl/rtl/otp_ctrl_scrmbl.sv
+++ b/hw/ip/otp_ctrl/rtl/otp_ctrl_scrmbl.sv
@@ -291,7 +291,7 @@
               key_state_sel  = SelDigestConst;
               data_state_en  = 1'b1;
               key_state_en   = 1'b1;
-              is_first_d     = 1'b1;
+              is_first_d     = 1'b0;
               digest_mode_d  = StandardMode;
               sel_d          = sel_i;
             end